1. Field
Example embodiments generally relate to Boiling Water Reactors (BWRs) and assemblies and methods for reinforcing piping for coolant spray within such reactors.
2. Description of Related Art
Generally, BWRs include a reactor core surrounded by a shroud and a shroud support structure. Piping typically penetrates this shroud to deliver emergency coolant water to the core in the event of an emergency involving a loss of coolant or where coolant is otherwise unavailable to the core.
As shown in FIG. 1, such piping includes core spray piping 10 and spargers used to deliver coolant water to the reactor core. The core spray cooling water is typically supplied to the reactor core region through a sparger T-box 15 that penetrates the shroud wall. The distal end of the T-box 15 is inside the shroud, while the proximal end extends outside the shroud.
The sparger T-box typically intersects two sparger pipes 10 to form a piping “T.” The sparger pipes 10 are typically welded to the sparger T-box 15. The distal end of the T-box 15 may be capped by a flat cover plate 20 welded to the T-box 15. While only a lower sparger T-box 15 is shown in FIG. 1, upper sparger T-boxes are typically present as well and roughly match the configuration of the lower sparger T-box in the upper configuration. Lower T-boxes typically intersect sparger pipes 10 at a center vertical displacement such that the pipes 10 mate symmetrically with the upper and lower halves of the lower T-box 15. Upper sparger T-boxes may not intersect the sparger pipes 10 at a center vertical offset due to other structural placement and thus sparger pipes 10 may not symmetrically mate with the upper sparger T-box.
The cover plate weld 25 and sparger pipe welds 26 are susceptible to cracking due to the high temperature, high pressure, and variable chemistry water flowing around the T-box 15. Resulting damage to welds 25 and 26 may be accessible for repair and inspection within a BWR only during scheduled plant outages for refueling and repair. These outages typically occur at several month intervals, and thus components within the core, including welds 25 and 26, must remain intact for lengthy periods before being inspected and/or repaired.
Further, BWR core operating conditions include high levels of radioactivity due to fission occurring in the fuel rods. Radioactivity, particularly the neutron flux generated in an operating nuclear reactor core, degrades the material strength and elasticity of core components over time. Components within the core, including welds 25 and 26, are thus subject to premature brittling and cracking due to this radiation exposure. Accordingly, flow-induced vibration, lengthy operating cycles, and demanding water conditions coupled with radiation can cause the welds 25 and 26 to crack, particularly, by intergranular stress corrosion cracking. If cracks in welds 25 and 26 propagate circumferentially so as to completely disunion either the cover plate 20 or the sparger pipes 10 from the sparger T-box 15, uncontrolled cooling water leakage may result.
Further compounding the precarious nature of the sparger T-box welds 25 and 26 is their arrangement within the shroud among other components. Even during repair phases, workers may have only remote access to the sparger T-box 15 inside the shroud, and locating and repairing welds on the T-box may require increased expense, removal of other components, and worker hazards.
Related art sparger T-box repairs and clamps may use clamping mechanisms to relieve stress on welds 25 and 26 and provide redundant security in the case of weld failure. Sparger T-boxes 15 may have various physical configurations based on their particular plant installation and repair history. Related art repair mechanisms are generally configured for only a single sparger T-box in a particular BWR and are incompatible with other sparger T-boxes in other BWRs.